1. Field of the Invention
The present invention relates to an image-size varying apparatus which varies, for example, the size of a display image in the horizontal/vertical direction, an image-size varying method, and a monitor apparatus comprising such an image-size varying apparatus.
2. Description of the Related Art
In recent years, as display apparatuses for displaying and outputting an image for a computer apparatus, the use of display apparatuses with a CRT (Cathode-Ray Tube) as a display device have become widespread. Generally, such a display apparatus has the function such that the size (image size) of a display image can be varied by a user as desired by varying the length (horizontal size) of an image displayed on a tube surface along the horizontal direction thereof and the length (vertical size) thereof along the vertical direction. When the display image is associated with a computer apparatus, the display image referred to herein refers to a desktop screen and a window screen displayed on the tube surface.
Such a function for varying the image size is known in which the horizontal size and the vertical size of an actual display image are varied by varying a parameter for controlling the variation of the horizontal size and a parameter for controlling the variation of the vertical size independently of each other for each step in such a manner as to correspond to the operation by the user. Or, a function for varying the image display area is known in which the image size is varied by simultaneously varying the horizontal size and the vertical size of the display image on the basis of a preset fixed ratio.
Meanwhile, depending upon the way in which a user will use it, a situation may naturally occur where there is a need to change the image size while, for example, the balance of the aspect ratio of figures, characters, and the like, drawn on the display screen is not distorted, that is, the original aspect ratio of the display image is maintained. However, in the above-described image-size varying method, it is difficult to vary as desired the image size while maintaining the aspect ratio of the display image, because of the factors described below.
One of the factors is an influence from hardware. For example, the amount of variation of each of the horizontal and vertical sizes of the actual image, corresponding to one step of the parameter control value for varying the image size, is determined by the configuration of the internal deflection circuit and the like, and differs, for example, from model to model. For this reason, even if, for example, the parameter control value is varied so as to simply enlarge or reduce by one step in each of the horizontal and vertical directions, the aspect ratio (the ratio of the horizontal size to the vertical size) of the display image after the size has been changed differs from the aspect ratio of the original display image.
Also, there is an influence from the difference in the active ratio of the display image with respect to the raster formed on the tube surface.
Here, the raster in this specification refers to an area formed on the tube surface as a result of deflecting an electron beam by a deflection yoke. The size (raster size) is the size of an interval corresponding to the interval such that the retrace interval is removed from the deflection cycle. Hereinafter, the size of the raster in the horizontal direction will be referred to as a horizontal raster size, and the size of the raster in the vertical direction as a vertical raster size.
Also, the active ratio refers to the occupied ratio (horizontal active ratio) of the display image in the horizontal direction with respect to the horizontal raster size, and the occupied ratio (vertical active ratio) of the display image in the vertical direction with respect to the vertical raster size.
For example, FIG. 8A shows a state in which a display image G having an active ratio (horizontal active ratio) of 50% in the horizontal direction with respect to a raster RS is displayed.
Assuming that, for example, the control value is updated so that the horizontal size of the display is enlarged by one step from the display state shown in FIG. 8A, since the monitor apparatus operates so as to enlarge the deflection width in the horizontal direction, on the basis of the control value, in a manner corresponding to one step, the horizontal raster size of the raster RS is enlarged by an amount of variation corresponding to one step.
As the horizontal raster size of the raster RS is enlarged in the manner described above, the horizontal size of the display image G formed within the raster RS is also enlarged. Since the horizontal active ratio of the display image G in this case is 50%, the horizontal size of the display image G is enlarged by an amount of variation corresponding to 0.5 step with respect to the raster RS.
FIG. 8B shows a state in which is formed a raster RS having a raster size and an aspect ratio that are different from those of FIG. 8A, and displayed is a display image G having the same size as that in FIG. 8A with respect to this raster RS. The active ratio of the display image G with respect to the raster RS in this case is assumed to be 90%.
In this case, it is assumed that the control value is updated so that the size is enlarged by one step in the horizontal direction in the same way as in FIG. 8A from the state shown in FIG. 8B. As a result, the horizontal raster size of the raster RS is enlarged by an amount of variation corresponding to one step. Since the horizontal active ratio of the display image G is 90% in this case, the horizontal size of the display image G is enlarged by an amount of variation corresponding to 0.9 step with respect to the raster RS.
As described above, since the active ratio of the display image G with respect to the raster RS differs, even if the number of steps by which the control value is varied is the same, the amount of variation of the size of the display image with respect to this number of steps differs according to the active ratio of the display image G with respect to the raster RS. Although in FIGS. 8A and 8B, a comparison is made in the same horizontal direction, a phenomenon similar to the above occurs also when the size is changed in units of one step in both the horizontal and vertical direction in the case where the active ratio of one display image with respect to a specific raster size is different between the horizontal direction and the vertical direction.
For this reason, in the case where, for example, the horizontal active ratio of the display image with respect to a raster size differs from the vertical active ratio thereof, even if, for example, enlargement/reduction is performed according to an amount of variation with the same number of steps in the horizontal and vertical directions, the result is that the amount of variation of the horizontal size of the display image differs from the amount of variation of the vertical size thereof. Therefore, the aspect ratio of the display image whose size has been changed differs from the aspect ratio of the original display image.
Further, as a factor which makes it difficult to vary the image size while maintaining the aspect ratio of the display image, in the current situation, there is a case in which an adjustment of the image size by the user exerts an influence.
For example, in such a case, in the monitor apparatus, it is assumed that the construction is formed such that the size of the image is varied according to a predetermined fixed ratio as the amount of variation in both the horizontal and vertical direction.
FIG. 9A shows a case in which the horizontal size and the vertical size of the raster are varied simultaneously based on a fixed ratio of 4:3 as an example of an amount of variation in the horizontal and vertical direction. That is, the number of steps of the control value required to vary the vertical size so that the amount of variation of the vertical raster size is three times as great, which will correspond to a number of steps of the control value required to vary the horizontal size so that the amount of variation of the horizontal raster size is four times as great, is determined in advance, and the horizontal and vertical raster sizes are varied simultaneously in accordance with these two numbers of steps.
In FIG. 9A, the raster RS is also assumed to have an aspect ratio of 4:3. It is assumed from this state that the raster RS is enlarged on the basis of a fixed ratio of 4:3 as an amount of variation of the horizontal/vertical raster size, as indicated by the broken line in FIG. 9A.
In this case, since the aspect ratio of the raster RS and the ratio of the size-varying amount in the horizontal/vertical direction are the same at 4:3, the aspect ratio of the display image G is maintained at a constant because the display image G formed on the raster RS is also enlarged at a ratio of 4:3 as the amount of variation of the horizontal size and the vertical size.
Further, in the monitor apparatus for a computer apparatus, a monitor apparatus capable of selecting a plurality of types of resolutions, commonly called a multi-scanning type, is in common use. However, there are cases in which the size of a raster and the aspect ratio of a raster, formed on the tube surface, are different depending upon the set resolution.
Further, in the case where the image size is varied in the conventional monitor apparatus, a method is widely used in which the image size is changed by varying the raster size in both the horizontal direction and the vertical direction independently of each other according to an operation by the user.
Accordingly, the user changes and sets the resolution, or performs an operation on the horizontal direction and the vertical direction independently, from the state shown in FIG. 9A, causing an aspect ratio different from the aspect ratio of 4:3 shown in FIG. 9A to be set as the aspect ratio of the raster. This state is shown in FIG. 9B.
FIG. 9B shows a case in which the aspect ratio of the raster RS is 1:1, as an example. Then, from this state, the image is enlarged as indicated by the broken line in the figure.
In this case, as described above, assuming that it is set that the horizontal size and the vertical size of the raster are simultaneously varied according to a fixed ratio of 4:3 as the amount of variation in the horizontal/vertical direction, if the image is enlarged at this fixed ratio, as shown by the frame of the broken line of the figure, the raster RS whose size has been varied becomes different from the aspect ratio which should be originally 1:1. Further, as a consequence to this, the display image G whose size has been varied is also displayed at an aspect ratio different from the original aspect ratio.
That is, even if a method for varying the image size at a fixed ratio is used, in the current situation, the above-described change of resolution and the independent adjustments of the horizontal/vertical size with respect to the image are performed by the user, and when the raster RS does not match the above-described fixed ratio, an inconvenience of the aspect ratio of the image becoming different occurs.
For example, regarding the resolution, the following is considered that the fixed ratio when the image size is varied is set and changed in such a manner as to correspond to each resolution prepared beforehand. Since some computer apparatuses have many types of resolution, however, it is not efficient to set a fixed ratio corresponding to all of these resolutions.
Accordingly, it is an object of the present invention, the achievement of which will solve the above-described problems, to make it possible to vary an image size while the aspect ratio of a display image is always maintained at a constant by absorbing the condition for the difference in the amount of variation in the horizontal/vertical size of the raster by hardware, the condition for the active ratio of the display image with respect to the raster size, the condition for the aspect ratio which is varied by the adjustment of the image size by an operation by the user, and other conditions.
To achieve the above-described object, according to one aspect of the present invention, there is provided a raster scan display apparatus for displaying an input video signal, the raster scan display apparatus comprising: first changing means for changing one length of an image display area along the horizontal or vertical direction thereof; computation means for computing the other length of the image display area along the horizontal or vertical direction after the size is changed by using the one changed length and the aspect ratio of the image display area before the size is changed; and second changing means for changing the other length of the image display area along the horizontal or vertical direction on the basis of the other length determined by the computation means.
According to another aspect of the present invention, there is provided a size changing method of changing the size of an image display area of a raster scan display apparatus for displaying an input video signal, the method comprising: a first step for changing one length of an image display area along the horizontal or vertical direction thereof; a second step for computing the other length of the image display area along the horizontal or vertical direction after the size is changed by using the one detected length and the aspect ratio of the image display area before the size is changed; and a third step for changing the other length of the image display area along the horizontal or vertical direction on the basis of the other computed length.
With the above-described construction, if, for example, only the information of a horizontal raster-size variable control value and the information of a vertical raster-size variable control value are given, the information of the aspect ratio of the actually displayed raster is obtained. Then, if the horizontal raster-size variable control value and the vertical raster-size variable control value are varied simultaneously so that this aspect ratio becomes constant, it becomes possible to perform the enlargement/reduction of the raster size while maintaining the aspect ratio at a constant.
The above and further objects, aspects and novel features of the invention will become more apparent from the following detailed description when read in connection with the accompanying drawings.